The process of landing an aircraft on an airport runway requires a good degree of skill as well as knowledge of the aircraft's position with respect to the runway. A pilot must be aware of the aircraft's speed, direction, and angle of descent (known as the glideslope) with respect to the desired touchdown location on the runway. Improper landings may occur if inclement weather or poor visibility, for instance, impedes the pilot's awareness of one or more of these factors.
Because of the possible difficulties that may occur during landing, various systems have been devised to assist the pilot. One such system is known as the Instrument Landing System (ILS), which in its most basic form comprises a VHF localizer signal and a UHF glide slope signal that are transmitted from different positions adjacent the runway. A receiver onboard an airplane receives the signals, and the signals are converted into data usable to determine the position of the airplane with respect to the runway centerline as well as the glide path of the airplane. The ILS signals, which combined may be termed an ILS beam, thereby provide the pilot with critical information that may be used during a landing, even in low-visibility situations.
Many airports cannot afford the equipment necessary to fully implement the ILS system so that it may be used in all weather and visibility categories of approved landing approaches. Some of these airports have deployed a less expensive ILS system that emits a lower-quality beam known as a Type I ILS beam. A Type I ILS beam may be suitable for assisting pilots to land in relatively clear weather, but lacks the integrity necessary to be used in the lowest visibility and weather conditions. Because a Type I ILS beam is unverified, it is possible that the beam may transmit incorrect data, and reliance on the incorrect data in poor visibility may cause an unsafe landing if the pilot cannot otherwise verify the data given to him by the ILS beam. For this reason, a Type I ILS beam may not normally be used to direct a pilot during a CAT II (defined as requiring a runway visual range of >1200 feet and a decision height of 100 feet) or a CAT IIIa (defined as requiring a runway visual range of >700 feet and a decision height of 50 feet) approach. What is needed is some way of increasing the integrity of a Type I ILS beam so that the beam may be used in low visibility conditions such as a CAT IIIa approach.
Global positioning systems, which use a constellation of satellites to provide location coordinates of an object, show significant potential to improve some avionics functions. In the future, some airports may use GPS-based landing aids to provide ILS-like lateral and vertical deviations from a desired approach path. An independent means to verify the GPS-derived path is needed to improve the overall integrity of the system.
It is therefore an object of this invention to provide a system that increases the integrity of a navigational aid such as an ILS beam or a GPS-based landing system.
It is another object of the invention to provide a system that independently verifies data derived from a navigational aid.
One feature of the invention is the use of data from an imaging system to independently verify data from a navigational aid.
Another feature of the invention is the creation of a geometric construct, representing geometries sensed by an imaging sensor, and the derivation of an aircraft's glideslope and position relative to a centerline of an airport runway.
An advantage of the invention is that low-visibility CAT IIIa approaches may be performed at airports having Type I ILS systems.
Another advantage of the invention is that unsafe landings are significantly reduced.